Cathode assembly



Jan. 14, 1941. R. B. AYE R CATHODE ASSEMBLY Filed May- 51, 1940 ill? A 9INVENTOR RAYMOND B. AYE/2 ATTORNEY Patented Jan. 14, 1941 UNITED STATESCATHODE ASSEMBLY Raymond B. Ayer, Verona, N. J assignor to RadioCorporation of America, a corporation of Delaware Application May 31,1940, Serial No. 338,189

7 Claims.

My invention relates to cathodes for electron discharge devices,particularly to supports and current supply means for cathodes in suchdevices.

Transmitter tubes of the type shown in the Zottu et a1. Patent2,113,671, April 12, 1938, employ a cage type cathode comprisingcircularly arranged parallel straight filament wires. When thesefilament wires are of pure metals such as tungsten or tantalum and areoperated at temperatures as high as 2000 C. or above, the problem ofinsulatingly supporting the cathode in fixed spaced relation with theother electrodes is diflicult. If mechanical supports are provided atboth ends of the cathode, provision must be made for expansion andcontraction of the file.- ment wires, and insulating bushings must beprovided to withstand the high operating temperature and yet permit freelongitudinal movement for the wires.

An object of my invention is a cathode with improved support means thatwill accurately fix the cathode in spaced relation with the otherelectrodes and will permit longitudinal expanson.

A more specific object of my invention is an improved cathode supportfor transmitter tubes of high power that is easy to assemble and willprotect insulating spacers from the high operating temperatures of thecathode.

The characteristic features of my invention are defined in the appendedclaims and one preferred embodiment thereof is described in thefollowing specification and shown in the accompanying drawing in whichFigure 1 shows in section my improved cathode and support mounted in atransmitter tube, Figure 2 is a longitudinal sectional view showingdetails of construction of my improved cathode support, and Figure 3 isan end view of the assembly shown in Figure 2.

The particular transmitter tube shown in the drawing comprises awater-cooled anode l, coaxial with a screen grid 2, a control grid 3 andcathode 4. The wires of the grids and cathode are straight and parallel,are circularly arranged, and lie in concentric cylindrical surfaces. Thefilament wires of the cathode are at their lower end 5 bunched togetherand joined as by arc welding or high temperature brazing.

Hollow lead-in conductors or pipes 6 and I sealed into the upper end ofthe envelope support the cathode and supply the heating current to thefilament wires. On the inner ends of the pipes are carried concentricmetal ring 8 and metal plate or disc l0. Preferably the plate is fiat,although the plate may be convexed or concaved, and preferably the rimof the plate lies in the plane of the ring although it may be axiallydisplaced with respect to the ring. The inner periphery of the ring isserrated with radial teeth or extensions 9 interleaved with serrationsII on the outer periphery of the disc. The serrations may be rounded asshown, triangular in shape or of any desired configuration which can beeasily formed in the ring and disc and fitted together without shortcircuit. Alternate filament wires 4 of the cathode are joined to theserration 9 on the ring, the other wires being joined to the serrationsH on the disc. To join the filament wires to the serrations, it ispreferred to bore holes in the serrations normal to the plane of thering and disc, with the holes arranged in a circle coaxial with thering. The

ends of the filament wires may then be inserted in the holes and, whenbrazed or welded in place, stand normal to the plane of the ring anddisc and accurately center the cathode in the tube.

According to one of the novel features of my invention, a cooling fluidis circulated in contact with the rear surface of the ring 8 and disc10, the cooling effect of the fluid being brought to the ends of thefilament wires. Since the ends of the filament wires are kept cool thewires will not bow or buckle and the brazed connections at the ends ofthe wires cannot be softened or loosened by heat. The ring 8 closes oneend of a hollow annulus l2 comprising two telescoped and coaxial spacedtubular walls I: and H. The interior of the annulus communicates withthe interior of the lead-in pipe 6 and is joined gas and liquid tight tothe end of the pipe. Pipe 6 has a central partition l5 that extends intothe annulus and abuts liquid tight at its end against the inner surfacesof cylinders l3 and I4 and ring 8. Cooling fluid, such as water,entering conductor 6 on one side of the partition then flows into andaround the annulus to the other side of the partition where it re-enterstube 6 and flows out. Pipe 1 is joined gas and liquid tight to the rearsurface of disc Ill and is provided with a central partition so thatcooling fluid flowing inwardly along one side of the partition isprojected against the rear surface of the disc and flows out along theother side of the partition. Alternatively, of course, a small feed pipecould be passed into pipe I and terminated short of the rear surface ofthe disc It to provide the inlet or outlet passage within the pipe I forthe cooling fluid. The inner end of the pipe I and disc I0 is heldcoaxial with and in fixed spaced relation from the inner cylinder [4 ofthe annulus by an insulating bushing I6 of refractory insulatingmaterial, such as ceramic.

Since the bushing l6 lies between the Watercooled wall of cylinder l4and pipe 1, and its end is shielded from the filaments by disc l0, itstemperature may never rise above the temperature of the cooling fluid,and a tight or drive fit may be made between pipe 1, bushing l6 andcylinder l4 since no provision need be made for expansion of the metalor insulating parts of the cathode support. A heat and electron shieldI1 may, if desired, be mounted on the ring 8 to prevent thermal andelectron emission from the filament wires to the grid wires.

All metal parts of my improved cathode support may be made of copper,nickel, Monel or other easily machined metal, and because of theirmechanical simplicity are easily assembled. Good results have beenobtained in making my improved cathode support with the ring 8 and discll] of nickel only in thickness. The holes in the serrations of the ringand disc are accurately bored on a drill press or lathe normal to thefaces of the ring and disc and the parts then assembled. The filamentwires of tungsten, about .05 inch in diameter, are then slightly taperedby caustic etching, inserted in the holes and arc-welded on the under orwater-cooled side of the serrations. Preferably the ends of the wiresare Pushed through the holes so that their ends appear on the reverseside where they can be arc welded or brazed.

I claim:

1. A cathode assembly comprising a, cylinder with two spaced concentricmetal walls, means for circulating a cooling fluid between the walls, aring, serrated along its inner periphery, in good heat conductingcontact with one end of the cylinder, a metal disc serrated along itsperiphery, in the plane of said ring and coaxial with the ring, theserrations of the disc extending radially outward and between theserrations of the ring, means supporting the disc in insulated spacedrelation from the ring, and a filament wire connected to each of theserrations.

2. A cathode assembly comprising an annulus, a metal disc coaxial withthe annulus, means for circulating cooling fluid against one side ofsaid disc, a plurality of circularly arranged parallel filament wires,alternate wires being joined at one end to the other side of said discand the remaining wires being joined at one end of the tubular annulus,said wires extending outwardly normal to the plane of said disc.

3. A cathode comprising a plurality of circularly arranged parallelfilament wires, current supply means for one end of the cathodecomprising a concentric metal ring and a plate, the outer periphery ofthe plate and the inner periphery of the ring being serrated with theserrations of the ring and plate interleaved, at least one filament wirejoined to each serration.

4. A cathode assembly comprising an annulus with two telescoped spacedtubular walls, said walls being closed at their ends, means forcirculating a cooling fluid between said walls, a pipe extending intoand coaxial with said annulus, a plate joined to the end of said pipeand fixed in a plane transverse to the axis of said annulus, aninsulating bushing between the outer wall of the pipe and the inner wallof the annulus, a filament wire joined at one end to the plate and asecond filament wire joined to the end of said annulus, the other endsof the wires being joined together.

5. A cathode assembly comprising a coplanar ring and disc, means forcirculating a cooling fiuid against one side of said ring, means forcirculating cooling fluid against the corresponding side of said disc, aplurality of filament wires on the other side of the ring and disc, someof the wires being joined to the ring, the remainder of the wires beingjoined to the disc, the other ends of the wires being connectedtogether.

6. A cathode assembly comprising a concentric ring and plate, a hollowannulus joined to one side of said ring, a pipe joined to one side ofsaid plate, interleaved serrations along the opposing peripheries of thering and disc, filament wires inserted at one end in holes in saidserrations, the opposite ends of said filament wires being mechanicallyand electrically connected.

7. An electron discharge device comprising a tubular anode and a coaxialcathode, said cathode comprising straight parallel circularly arrangedwires lying in a cylindrical surface coaxial with said anode, said wiresbeing mechanically joined together at one end, means for rigidlysupporting each wire in said surface comprising two hollow lead-inconductor pipes, a metal ring joined to the inner end of one pipe, ametal plate coaxial with the ring. joined to the end of the other pipe,the other ends of the wires being secured to said ring and disc, and aninsulating spacer for rigidly holding said ring and disc in fixed spacedrelation.

RAYMOND B. AYER.

